In many applications, such as in power plants, high temperature boiler feedwater systems require fluid valves having reliable valve fluid sealing components (i.e., valve trim) which is required to provide a tight fluid shutoff for long periods of time. Special problems arise in such environments in view of the high pressures and the high temperatures which can range from about 250.degree. to about 450.degree. Fahrenheit.
Presently available valves for such environments include complex shaped valve trim components which lead to costly manufacturing and time consuming and costly replacement during normal valve maintenance. Typically, fluid valves employ metal-to-metal seating for all general applications over a wide range of pressure drops and temperatures, and metal-to-TFE (tetrafluoroethylene) seating for more stringent shutoff requirements. An example of such a standard and optional seating is available in a design ES valve body made by Fisher Controls International, Inc. This commercially available fluid valve includes a valve trim having a valve plug seating against a seal ring formed of tetrafluoroethylene (TFE) which is located in a metal seal ring housing and held in place by a metal disk retainer. While such a configuration is acceptable for most conditions, it is desired to provide a fluid valve with improved valve trim components for reliable use under stringent high pressure and high temperature conditions.
In U.S. Pat. No. 3,809,362, there is described an improved valve trim for high pressure fluid valve use and wherein a deformable plastic insert seat ring is mounted on a seat ring housing and held in place by a seat ring retainer. The seat ring retainer includes a series of inwardly and outwardly formed surfaces facing opposite similarly shaped seat ring housing surfaces, and with the deformable plastic seat ring having a similar series of surfaces and located between the retainer and the housing. During valve closing, the valve plug compresses the deformable seat ring to stress the ring above the yield point and cause it to act like a liquid to enable the seat ring to deform and displace so as to establish a plastic-to-metal hydrostatic seal.
It is desired to provide a fluid valve having a valve trim which is capable of reliable operation under high pressure, high temperature conditions. It is also desired to provide such a valve trim which is more easily manufactured and at less cost than presently available units and which can be more easily and readily maintained during normal valve maintenance.